This application requests continuing support for a long-standing study on analysis of the cariogenic properties of S. mutans using a combination of genetic and molecular techniques. A major focus of the proposed work continues to be on the role of the various glucosyltransferase (GTF) enzymes on polysaccharide synthesis and on bacterial colonization and accumulation on the tooth surface. In particular, various GTF derivatives constructed by site-directed mutagenesis, by recombination between different GTF genes, and by chemical oligomerization of monomers will be analyzed for in vitro biosynthetic activity, for their effects on sucrose-dependent adhesion of S. mutans, and in order to determine the glucan-binding domains of the enzymes more precisely. In addition to these biochemical studies, the Principal Investigator proposes to follow up on some interesting preliminary work done during the current funding period, and to carry out molecular and genetic analysis of the effects of low pH on the transcriptional regulation of GTF genes and additional genes to be identified in the proposed funding period. Finally, the Principal Investigator proposes to improve a heterologous protein secretion system, employing S. gordonii that has been developed in his laboratory, and to use the system to express a putative adhesion domain of a P. gingivalis protein in order to begin in vitro studies to assess the potential use of the S. gordonii strain as a biological agent to be implanted in the oral cavity to antagonize colonization by pathogens.